In the field of clinical diagnostics it is necessary to obtain samples of body fluids, in particular blood samples, in order to detect constituents thereof. If a larger amount of blood is required, it is usually collected with a syringe or similar device by piercing a particular blood vessel. However, the field of the present invention is one in which only small amounts of sample in the range of a few microliters (μl) or less are necessary to determine analytical parameters. Such a procedure is especially widespread for measuring the blood sugar level, coagulation parameters, triglycerides, HBA1c, or lactate.
In the field of diabetes it has now become accepted practice for diabetics to monitor their blood sugar level (so-called home-monitoring). This is necessary to maintain a blood sugar level which is within the normal range by administering calculated doses of insulin. If a diabetic becomes hypoglycaemic he may become unconscious possibly resulting in the death of the patient. If, on the other hand, a patient has a blood sugar level which is too high, this can lead to serious secondary effects such as loss of sight and gangrene. Small and easy-to-handle blood withdrawal devices, so-called lancing aids that can be simply and reliably operated by the user or hospital and nursing staff are now commonly used to withdraw the blood required to measure the blood sugar level. Recently systems for withdrawing interstitial fluid have also been disclosed which can in principle be used to carry out such analyses.
An emerging problem in this field is contamination and injury by used lancets. In many commercial devices the lancet is removed or ejected after the lancing process. The needle of the lancet which is exposed in such cases can lead to injuries that may result in infections. Consequently in some countries attempts are already being made to prohibit blood withdrawal systems in which the needle tip is freely accessible after use.
Various variants of blood withdrawal systems have been described in prior art documents in which the needle is protected after the lancing process. A cap in which a lancet is located is described in U.S. Pat. No. 5,314,442. In order to carry out a lancing process, the lancet is pushed within the cap by a plunger or a similar device in such a manner that the needle exits through an opening. After the piercing the lancet is retracted inside the cap and flexible elements on the lancet ensure that the lancet needle can no longer emerge without the action of the plunger. Systems based on a similar principle are described in U.S. Pat. Nos. 4,990,154 and 5,074,872 and PCT Application WO 00/02482. Another system in which a lancet is retracted into a cap by an incorporated spring is described in German Patent No. DE 198 55 465. Although the said documents already solve the problem of contamination or injury to the user, within the prior art the drive mechanism is only coupled to the lancet by a press fit. The puncture depth of the needle is limited by a stop. However, it has turned out that the lancet impacting on the stop vibrates the needle which increases the pain caused by the puncturing. This problem is described in more detail in European Patent No. EP 0 565 970.
An object of the present invention was to suggest a system for withdrawing body fluid which, on the one hand, avoids contamination or infection by used lancets and, on the other hand, allows a substantially pain-reduced lancing for the user. Another object was to simplify the systems of the prior art and make them more cost-effective and, in particular, to propose a design which can be miniaturized. The latter is especially important in order to provide a system that operates with lancets in magazines and allows a user to change a lancet that has not yet been used without having to carry out complicated handling steps.
The said objects of the present invention are achieved by embodiments of systems for withdrawing body fluid which have a drive unit with a plunger which is moved from a resting position into a lancing position in order to carry out a lancing process. The systems also comprise a lancing unit in which a lancet with a needle is located adjacent to the plunger in its resting position, and is arranged within the lancing unit so that the needle is displaced by the plunger when it moves into the lancing position in such a manner that the needle at least partially emerges from the lancing unit through an outlet opening. An important feature of the system is that the plunger and lancet are interconnected by a form fit in order to carry out the piercing process.
A characteristic feature of a form fit in the sense of this invention is that it enables the lancet and driving plunger to be coupled with little expenditure of force. There are two basic ways for achieving a form fit. In a first variant the lancet and driving plunger are coupled by close fitting in such a manner that a holding element is enclosed. The form which closes is referred to as a holding device within the scope of the invention. If the holding device is located on the lancet, the driving plunger has a holding element, but if the holding device is on the driving plunger, the holding element is located on the lancet. FIGS. 1 and 2 show practical embodiments. This variant of the form fit is preferably achieved in that a longitudinal movement in the piercing direction causes a transverse movement of the holding elements of a (initially opened) holding device which thereby close around a holding area.
The holding element is preferably (at least partially) gripped from behind when the holding device closes in such a manner that the lancet is carried when the driving plunger is pulled back—at least to a possible opening of the holding device. Furthermore, it is preferred that the geometry of the holding device and holding area match in such a manner that there is no movement or only a slight movement in the direction of the lancing movement after the form fit and that the movement of the driving plunger in the lancing direction as well as in the opposite direction is converted without any play in the movement of the lancet. This can be achieved when the longitudinal extension of the chamber in the closed holding device is identical to or only negligibly larger than the longitudinal extension of the holding area (see FIG. 1). In another embodiment of this variant the longitudinal extension of a recess in the holding area and holding elements on the holding device correspond in such a manner that transport in the lancing direction is possible without essentially any play (see FIG. 2).
In a second variant of the form fit, the holding device and the holding area are essentially dimensionally stable and the holding area is enclosed by the holding device. The profiles of these two units move into each other. Since the units are dimensionally stable, a complete enclosure is not possible and the profiles must be open to such an extent that they can be moved into each other. This joining movement (of at least one path component) is at right angles to the lancing direction resulting in a connection which is also essentially without any play in the lancing direction (see FIG. 4). Finally, coupling can also be achieved by a movement having components at right angles as well as parallel to the lancing direction (see FIG. 7).
The system according to the invention for withdrawing blood has a drive unit with a plunger which moves a lancet from a resting position into a lancing position. A number of drive mechanisms are known from the prior art that can be used in the field of blood withdrawal devices. In particular, drive mechanisms are used on a large scale which obtain their energy from a previously tensioned spring. Drive units are preferably used within the scope of the present invention which enable a guided movement of the plunger and the lancet as a result of the form-fitting connection. A guided movement means that the lancet pierces the body over a predetermined path and is also removed from the body over a predetermined path-time course. In conventional systems of the prior art based on a combination of a spring and a stop the path-time course is influenced by numerous parameters such as manufacturing tolerances (frictional conditions in the system, strength of the spring, etc.) as well as the skin surface. It has turned out that a guided movement of the lancet, for example, by means of a guide block as described in European Patent No. EP 565 970, is advantageous with regard to the pain caused by the piercing. With regard to the drive unit, reference is herewith made to the preferred drive mechanisms of European Patent No. EP 565 970 and its U.S. counterpart, U.S. Pat. No. 5,318,584, the disclosures of both which are herein expressly incorporated by reference, and U.S. Pat. No. 4,924,879.
An important aspect of the invention is a lancing unit containing at least one lancet that can be removed from the drive unit. The lancing unit comprises a housing in which the lancet is arranged in a resting position. This prevents the lancet from causing injury or being contaminated before or after use. The housing can be designed such that a single lancet is located therein or the housing can have the form of a magazine containing a plurality of lancets. Usually the lancets in a magazine are located in separate chambers to prevent contamination of unused lancets by ones that have already been used. The housing of the lancing unit is designed such that it can be attached to the drive unit. For this purpose the lancing unit can, for example, have the shape of a cap which is mounted on the drive unit. Such embodiments are described, for example, in U.S. Pat. Nos. 5,314,442, 4,990,154 and 5,074,872, the disclosures of all which are herein expressly incorporated by reference.
Embodiments are also possible in which the lancing unit is permanently connected to the drive unit or is an integral component of the drive unit. This can be used for systems with a magazine such that the entire unit can be discarded after the magazine has been used. In the case of a lancing unit in the form of a magazine, it can, for example, have chambers arranged next to one another in which the lancets are located and the chambers are positioned successively relative to the drive unit such that the lancets can be coupled to the plunger of the drive unit. A magazine in the form of a barrel having chambers arranged parallel to the longitudinal axis of the barrel in which the lancets are located is another possible embodiment. In a similar manner to a revolver barrel, such a magazine can be repeatedly attached to the drive unit.
Another requirement for the lancing unit is that the sterility of the lancets must be ensured over a long time period. The lancing unit can be sterilized by gamma irradiation, which is commonly used in the prior art. In order to maintain the sterile conditions, the lancing unit can be sealed in an enclosing package, for example, a polyethylene bag. In another embodiment, the openings of the lancing unit (for inserting the plunger and for the exit of the needle tip) can be closed by sealing foils. These can, for example, be detachable sealing foils that are removed by the user before use. However, thin foils can also be used which are pierced before use by the plunger or by the needle tip so that the user does not have to carry out additional handling steps. Such foils can be manufactured as a part of the manufacturing process for the lancing unit, which is usually an injection moulding process.
In another embodiment, the needle tip is protected from contamination by an elastomer, which is removed before the lancing or is pierced during the lancing process in order to expose the needle tip. Such a protection of the needle from contamination is described in the PCT Published Application No. WO 01/66010, the disclosure of which is herein expressly incorporated by reference.
One or more lancets with a needle are located within the lancing unit. Apart from devices that may be present on the lancet that enable a form-fitting connection to a plunger, lancets can be used within the scope of this invention that are well-known in the prior art. Such a lancet usually has a main body made of plastic in which a metal needle is located. However, lancets without a separate main body are also possible (such as metal needles having a thickening at the rear end used as a holding area).
An important aspect of the invention is that the plunger of the drive unit and the lancet for carrying out the lancing process are connected together by a form fit. In this respect the invention differs substantially from the prior art where the lancet and drive are mechanically coupled by means of a press fit (for example, U.S. Pat. Nos. 5,314,442, 4,990,154, and 5,074,872), a locking device (PCT Published Application No. WO 00/02482), by clamping (U.S. Pat. No. 3,030,959) or by simple pressure (German Patent No. DE 198 55465). A form fit is characterized in that a mechanically reliable coupling occurs between the drive and the lancet without having to apply a substantial pressure on the lancet in the direction of the lancing movement.
In the devices of the prior art which work with a press fit, a spring element (e.g. German Patent No. DE 198 55 465) or a retaining element (e.g. PCT Published Application No. WO 00/02482) have to be provided in the cap which contains the lancet. This element is designed such that the lancet does not emerge from the cap when the lancing unit is coupled to the drive unit.
However, spring elements in the lancing unit increase the manufacturing costs which is particularly serious since the lancing unit is a consumable. Furthermore, the drive unit requires an additional force to overcome a retaining element which also leads to vibrations of the needle which have an adverse effect on the puncturing pain. In addition, a guided movement which comprises a retraction of the lancet is problematic in systems which utilize a press fit since this can detach the press fit. Although the locking device described in PCT Published Application No. WO 00/02482 is directed to this problem, it is difficult to accomplish technically. In particular, it is difficult to establish such a locking device in a continuous manufacturing process since even slight variations in the material or the process conditions can result in a loss of the function of the device.
Another characteristic of the device described in PCT Published Application No. WO 00/02482 is that the locking occurs in a path range which serves to puncture the body. The fluctuations in force occurring during the locking and the vibrations have a disadvantageous effect on the pain of incision. Another characteristic of the device is that the needle remains in the body after the incision and is not actively retracted. The needle is only retracted when the cap is removed from the drive mechanism. In contrast, a form fit between the driving plunger and lancet according to the present invention enables the plunger and lancet to be connected without having to apply a particular force in the direction of the puncture. The form-fitting connection can be utilized to actively retract the needle after the incision. This ability to actively control the path-time curve of the needle by means of the drive unit enables the lancing to be carried out with very little pain.
Another property of the form fit according to the invention becomes apparent by examining U.S. Pat. No. 3,030,959. In an apparatus according to this U.S. Pat. No. 3,030,959, needles which are arranged in a tube are held successively by a clamping device which is similar to a propelling pencil. In addition to the contamination problems caused by used needles, which are not solved by this apparatus, the positioning of the needles in the axial direction (i.e. in the lancing direction) is not defined. In the same way as the length of the protruding pencil tip can be freely selected by the user in the case of a propelling pencil, the axial positioning of the needle depends on the adjustment by the user. In contrast, in the present invention the lancet and drive unit have matching holding areas and holding devices to create a form fit. The geometric design of the holding area and holding device enables the axial positioning of the lancet to be defined and thus enables an exact control of the puncture depth. Thus the use of a form fit avoids a force peak in the axial direction when the lancet and driving plunger are coupled together and also enables an exact axial positioning. In the case of a form fit, a form (holding device) encloses another form (holding area). In this sense “enclosing” means a movement of parts of the device at right angles to the lancing direction and alternatively a form fitting interlocking of two shaped bodies whose shape does not change.
In a preferred embodiment, the holding device is open and closes around the holding area when it is inserted into the holding device. This enclosing can occur, in particular, as a result of a longitudinal movement which is converted into a transverse movement of the holding elements of the holding device which are at right angles to the longitudinal direction of movement. One method of achieving this conversion of a longitudinal movement into a transverse movement is to insert or slide the holding device by means of the longitudinal movement into a tapered channel (e.g. into a sleeve) (see FIG. 1). In this connection, tapered not only refers to continuously tapering channels, but also to channels whose inner width decreases in the longitudinal direction. In this connection a channel does not have to be a body with a closed circumferential surface. If, for example, the holding device has two opposing hooks as shown in FIG. 1, it only requires two walls whose distance to one another decreases.
Another possibility is to close the holding device by releasing a tensioned spring (see FIG. 2) which can, for example, be achieved by moving the holding device in a broadening channel.